The long-term goal of this proposal is to explore how the steroid hormone estrogen (E) regulates growth and differentiation processes in the endometrium during early pregnancy (preimplantation period), which lead to acquisition of the receptive state that allows blastocyst implantation. E exerts its cellular effects by regulating the expression of specific target genes. The identity, profile of expression, and function of the E-regulated genes at various stages of the reproductive cycle and pregnancy, however, remain largely unknown. The specific aims of this proposal are to: 1. Isolate and identify genes that are regulated in response to nidatory E in rat uterus during delayed implantation. The messenger RNA differential display method will be used to isolate and identify the cDNAs representing mRNAs whose expression is induced or repressed in rat uterus in response to an implantation-inducing dose of E. To determine whether the newly identified E-regulated genes are potential modulators of implantation, their spatio-temporal expression in rat uterus during early pregnancy will be analyzed by Northern blotting, in situ hybridization, and immunohistochemistry. 2. Assess the functional roles of the newly identified cDNAs in implantation. A recently developed antisense technology will be used to regulate specific gene expression in intact rat uterus. This will involve administration of antisense oligodeoxynucleotides targeted against mRNA transcript of each candidate gene into the preimplantation uterus to suppress the steady state level of that mRNA . If this intervention also leads to an impairment in implantation, it will allow the establishment of a functional link between this gene and the implantation process. 3. Analyze the function of a novel E-regulated gene, ERG1, in early pregnancy. A novel gene (ERG1) that is tightly regulated by E in two key reproductive tissues, the uterus and oviduct, has recently been isolated. ERG1 is expressed in the surface epithelium of the uterus in a highly stage-specific manner during the ovarian cycle and early pregnancy. To determine the functional role of ERG1 during early pregnancy, mice harboring a targeted germ line mutation of ERG1 will be developed and analyzed for potential reproductive phenotypes, such as impairment in embryo transport through the oviduct, defects in epithelial cell morphology and function, and lack of uterine receptivity for implantation. The proposed research will help us to identify molecules that mediate E regulation of critical events during early pregnancy.